Find matrix rows that have 3 common values, store the rows and the values

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Pseudoscientist 2019-4-16

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https://ww2.mathworks.cn/matlabcentral/answers/456694-find-matrix-rows-that-have-3-common-values-store-the-rows-and-the-values

编辑： Matt J 2019-4-17

Suppose I have a 500000x5 matrix and for each row I need to find rows that have 3 common elements within the first 4 elements of the row but different 5th element and store the common values and the sum of the 5th elements to a new matrix.

For example:

1 2 3 4 1

1 2 3 5 2

Would yield a row like this in a new matrix

1 2 3 3

Of course this could be done with 2 nested for loops and if statements but the calculation takes like 10 hours. I need something that takes a few minutes even with 500k rows.. Is this possible with Matlab?

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Pseudoscientist 2019-4-16

Yes the following result is correct, displayig the result in ascending order is very good

Matt J 2019-4-16

OK, see my answer then.

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采纳的回答

Matt J 2019-4-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/456694-find-matrix-rows-that-have-3-common-values-store-the-rows-and-the-values#answer_370870

编辑：Matt J 2019-4-17

在 MATLAB Online 中打开

I'll call your original 5 column matrix A.

 D=cell(4,1);
 a5=A(:,5);
 As=sort(A(:,1:4),2);  
 
 for i=1:4  %small loop
    
   Triangles{i}=  [As(:, setdiff(1:4,i)),a5];
   
 end
 Q=cell2mat(Triangles);
 result=consol(Q(:,1:3),Q(:,4));
 
    function out=consol(B,b)
    
       
       [C,~,j]=unique(B,'rows');
       nc=size(C,1);
       c=accumarray(j,b,[nc,1]);
       out=[C,c];
        keep=histcounts(j,1:nc+1)>1;
        out=out(keep,:);
    end

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Pseudoscientist 2019-4-17

编辑：Matt J 2019-4-17

Hmm quite interesting, the logic seems to work but when the results are plotted, the result is not that great..

Imagine a sphere filled with a tetrahedral mesh, the tetras have values 1 and 2. Now where the tetras face each other, we should have a triangular surface of values 3.

The first image is what should be. The second image is what is calculated as triangles with values 3. The third image is the sphere.